The present invention relates generally to a method and apparatus for cutting funicular material such as tow and monofilaments into short lengths.
Problems of cutting filamentary linear materials at high rates of feed are well known in the art. Glass fibers, carbon fibers and metallic fibers, in particular, as well as all of the higher modulus synthetics are troublesome to cut into accurate, usable staple.
Knives travelling at high speed striking an elastomeric surface, bedplate or other knives create turbulence, impact noise, and vibration which produce a highly objectionable environment around cutting equipment. Also, high speed impact results in fiber fusing and generally poor performance. Additionally, knives are usually made of hardened materials which are subject to fracture and present a safety hazard to both fiber manufacturing and fiber usage personnel. In this way, a fractured knife could possibly damage fiber processing machinery. Fractured knives cause multiple lengths of stable, poor fiber performance and machine down time.
Heretofore, the known cutting machines have not been capable of handling very high rates of feed while incorporating a slow cut, nonfusing, flying shear action. The glass fiber and hot melt fiber industries have been hamstrung by the lack of such equipment and have been forced at attenuate or stretch the semi-molten fibers at quite low rates of feed or alternatively, to employ separate heating steps. A cutting machine capable of at least 20,000 feet per minute would make intermediate energy wasting fiber processing steps unnecessary. The hot melt fibers could then go from a reactor to cut staple in one step and the glass fibers, attenuated by the cutter itself, could be run at the maximum speeds permitted by the spinning equipment. In this case, the cutter would no longer be the production bottleneck, and development could begin anew on increasing the spinning speeds.
An example of a prior art cutting device is disclosed in U.S. Pat. No. 3,485,120 issued on Dec. 23, 1969, to Keith. The Keith patent discloses a cutter which has a rotating cutting reel containing knives and a rotating pressure applicator. The material is built up around the cutting reel to be forced by the pressure applicator against the knives and cut into sections equal to the distance between the knives.
Another prior art cutting device is disclosed in U.S. Pat. No. 2,791,274, issued on May 7, 1957, to Rivers, Jr. The Rivers, Jr. patent discloses a rotating roll consisting of two pieces between which the fiber to be cut is trapped and rotated therewith until reciprocating knives in one piece and moved to cut the trapped fiber.
U.S. Pat. No. 3,978,751, issued on Sept. 7, 1976, to Farmer et al discloses (in FIG. 16) a center feed to a rotating camming assembly and a rotating driving disc containing a plurality of knives. The disclosure teaches rotating the driving disc and knives faster than the camming assembly. Cutting occurs when the tow band is peripherally clamped between a belt, or cam, and the knives.
Other U.S. patents which illustrate the state of the art in staple cutting include U.S. Pat. Nos. 4,014,231; 3,861,257; 3,869,268; 3,948,127; 3,557,648; 3,815,461; and 3,768,355.
Present glass fiber cutting equipment takes into account the rapid dulling of the knives and the necessity for short runs and excessive down time. The industry is in great need of equipment which will increase runs from hours to days or even weeks. Also, present metal fiber cutting equipment does not "cut" at all, but instead pulls the fibers in two. Short cut wire and monofilament staple are usually cut on slow punch press cutters. These procedures result in a random staple length having poor end conditions.
Accordingly, it is a primary object of the present invention to provide a method and apparatus which cuts funicular material at a rapid rate into segments having a uniform length.
Specifically, an object of the present invention is to reduce the high impact at the cut point and thereby reduce the possibility of knife breakage and also reduce vibration and noise.
A further object of the present invention is to provide a cutter which will not fuse the fibers together due to heat buildup at very high rates of feed.
A still further object of the present invention is to provide a cutter which will produce uniform and highly accurate cut lengths.
Another object of the present invention is to produce a cutter which sharpens the knives as the cutter is in operation. This self-sharpening feature has the advantages of reducing maintenance and increasing running time for the apparatus.
These and other objects are realized by the apparatus according to the present invention wherein a cutter comprises two closely spaced members, preferably rotors or discs facing one another. At least one of the rotors has a plurality of knives attached to its surface in a pinwheel configuration. In a preferred embodiment, both rotors have knives affixed to their respective surfaces in sliding contact engagement. One of the rotors preferably has at least one less knife than the other rotor. The rotor with the lesser number of knives rotates slightly faster than the other rotor. Attenuation (as in the production of glass or drawn fibers) or tension on the tow band (in the production of other fibers) is accomplished by weaving the tow band zigzag fashion into the spaces formed by the tapered knives on the two relatively sliding pinwheels. In this way, tow band pulling tension begins at the point of entry into the pinwheel niche proper and the tow band can slide down between the knives.
The tow tension builds as each set of knives comes nearer to a configuration of cutting mesh. Actually, the first set of knives (at tow band entry) is in maximum mis-mesh while the intermediate sets of knives are in varying degrees of mis-mesh, and the last set of knives to touch the tow is in complete cutting mesh. Cutting then occurs and the cut bundle, urged by centrifugal force and air (or other suitable medium), escapes from the machine and is flung into a product collector chute.
The present invention is capable of cutting substantially all fibers, but is especially adapted to glass, carbon, metallic and other fibers including wire and different generic monofilaments that, for one reason or another, have heretofore been considered exceedingly difficult to cut. The principle of conventional scissors has been employed at the point of severance of the present invention in a novel manner. The scissors action provides a certainty of cut and also a built-in self-sharpening feature for the apparatus that insures that many additional hours of satisfactory operation can be expected before normal sharpening of the knives by grinding is necessary. In the present invention, the knives grind themselves much like a butcher sharpens his knife.